Fast Local Tone Mapping for 10-bit ARRI LogC with flicker suppression
Updated:
Author: Fyodor Serzhenko
Tags: HDR, Fast Local Tone Mapping, ALTMapper, ARRI, LogC, Shadow Recovery, Flicker Suppression
ARRI Alexa cameras and ARRI LogC encoding are a professional standard on film and commercial sets. LogC packs a very wide dynamic range into a flat logarithmic curve: it looks washed out straight out of camera and has to be developed into a display image. The hard part is recovering shadow and highlight detail and delivering a pleasing Rec.709 picture — without halos, amplified noise, or the real problem on moving footage, flicker between frames.
Local tone mapping with ALTMapper
ALTMapper adaptive local tone mapping on GPU: shadows recovered, colors stable, no flicker, faster than real time.
We ran our ALTMapper adaptive local tone mapping algorithm on real ARRI Alexa LogC footage (ProRes 422 HQ, 10-bit) to show two things at once: the visual quality of local tone mapping, and the processing speed, which is significantly faster than real time. Performance is the classic bottleneck for local tone mapping, and it is exactly where a GPU implementation changes the picture.
Plenty of tools can produce a good local tone mapping result. What is hard — and what this test is really about — is doing it at speed: high quality and faster than real time at the same time.
The footage was shot by Sergey Chorniy and is publicly available; we were not able to reach the author directly.
Source footage: ARRI Alexa LogC, ProRes 422 HQ, 10-bit, 1080p24. The original is a large ProRes file, and browsers cannot play ProRes inline, so it is offered as a direct download rather than an embedded player. The clips here are web-friendly MP4 versions of the same shot.
A single frame from the original ARRI LogC footage — flat and low-contrast by design; this is the starting point for tone mapping.
For comparison, here is the same ARRI LogC shot without tone mapping and with DaVinci Resolve 20 — watch the shadow areas and the transitions between frames against the ALTMapper result above.
Rec.709 without tone mapping
Straight LogC to Rec.709 conversion, no tone mapping: shadows stay crushed and detail is lost.
Tone mapping in DaVinci Resolve 20
DaVinci Resolve 20 native tone mapping, shown for reference.
See it on your own images
Send us a few of your own frames — RAW, TIFF, JPEG or PGM — and we'll run ALTMapper on them, so you can judge the result on your own data.
Why this is hard on video
Local tone mapping computes its parameters from each region of each frame. A naive implementation lets those parameters drift and oscillate from frame to frame, which shows up as brightness pulsing, crawling shadows and flicker — and it also hurts compression, because the codec spends bits on the flicker instead of on real detail. ALTMapper keeps the local parameters temporally stable, so the graded footage stays smooth. We explain the temporal-stability problem in more depth on the local tone mapping on GPU page.
What ALTMapper delivers on this footage
- Shadow and highlight detail preserved — dark areas are opened up while the highlights are held, so nothing is crushed or clipped.
- Natural, stable colors — no color shifts or saturation swings from frame to frame.
- Smooth motion without artifacts — no halos trailing bright edges as the camera moves.
- No flicker on the final video, thanks to temporal stability of the algorithm.
Performance: speed is the point
Local tone mapping of this quality is normally an offline, render-time operation — the algorithms are heavy, and performance is their well-known bottleneck. ALTMapper runs about 6.3 ms per 65 MPix frame on an NVIDIA GeForce RTX 4090, over 10 gigapixels per second, which means real-time 8K on a single GPU, comfortably faster than the footage plays. That is what lets it sit inside a live camera ISP instead of a render queue.
To our knowledge, we have not seen another local tone mapper reach these speeds in real time at comparable quality. Full benchmarks and hardware details are on the local tone mapping on GPU page.
Other Use Cases
ALTMapper algorithm on the NVIDIA GPU is utilized in the following software:
- Fastvideo SDK for Windows/Linux/ARM
- Fast VCR software for real time camera applications
- Fast CinemaDNG Processor for offline RAW image processing
Some of our customers have already embedded that local tone mapper into their solutions for high performance raw processing.
References
- ALTMapper: Adaptive local tone mapping algorithm on GPU
- ALTMapper software: GUI and CLI application (free demo)
- RAW to RGB conversion on GPU
- FastVCR software on GPU for XIMEA cameras, Windows/Linux/ARM
- Deterministic ISP — AI-free, reproducible RAW-to-RGB (no invented pixels)
For cinema and post-production this means broadcast-quality tone mapping that runs faster than real time and fits into a live pipeline. ALTMapper is available in the ALTMapper software (GUI and CLI, free demo) and the Fastvideo SDK.
About the author
Fyodor Serzhenko, PhD, is the founder and CEO of Fastvideo. He earned his PhD at the Moscow Institute of Physics and Technology (MIPT) in 1993. Since 2009 he has led the development of Fastvideo’s GPU-accelerated image codecs and ISP modules, including the Fastvideo SDK. Connect on LinkedIn.
Why you can trust these results
Fastvideo has built GPU-accelerated image processing software since 2009. Our codecs comply with the standards they implement — JPEG (ITU-T T.81 / ISO IEC 10918) and JPEG2000 (ITU-T T.800 / ISO IEC 15444) — and our tools are open source on GitHub. Every performance figure we publish is reproducible: see our benchmark methodology, download the Fastvideo SDK benchmark report (PDF), and measure it on your own GPU.